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## Thursday, 19 August 2021

### Let's Stick Together...

Sometimes, all it takes to change the world is two simple words...

In recent days and weeks, while much of the world seems off to some sort of apocalyptic race to the bottom, with wildfires and flooding seemingly ubiquitous, a global health crisis enormously exacerbated by a lunatic campaign of disinformation and the political and geopolitical landscape (and, in Haiti, the actual landscape) increasingly in turmoil, something seems to have slipped slightly under the radar that may provide a ray of hope on at least one front. Maybe. If we can find two words.

Recent events in the global climate - literal rather than figurative - have caused a huge amount of consternation. As a close watcher of all areas of really important science for many years, I've seen something in recent weeks entirely new in my experience. Although entirely aware it was inevitable, it still came as a shock to somebody used to caution - sometimes even to the point of uncomfortable equivocation - when scientists talk about their conclusions.

What is this momentous event?

Climate scientists have unequivocally declared weather events to be a direct result of global warming.

That may not seem like a big thing but, to somebody very much used to hearing scientific conclusions couched in a necessary uncertainty that reflects the inductive nature of all science, it's huge. This simply isn't something scientists do without enormous evidential justification.

To put this in perspective, when I look at papers that interest me in particle physics, especially about cutting edge research, there's a number that I always look for. That number is denoted by the Greek letter Sigma $\sigma$. The Sigma is an indication of confidence. In general terms, to reach a confidence level of $5\sigma$ - the level required to declare a discovery - requires the accumulation of oodles and oodles of signals, all consistently hitting the predicted numbers for the particle of interest. At no point can we ever point to a specific particle and say 'that, right there; that's a Higgs'.

Similarly, with weather events under normal circumstances, we can't ever say unequivocally that a specific weather event is or is not a result of climate change, because weather is local events, while climate is global trends. Weather events are the particles in our LHC, while the climate is the trend of conditions in ATLAS, or CMS, for example.

But now there's something different happening, and we're quite rightly very concerned. The records of the last two years, and this year in particular, are significantly above what our models predict they should be on the trend data alone. This is unexpected.

It's important to be clear about what this means. Climate models have consistently shown a trend upwards. That isn't at all a surprise to us. What's a surprise is how far beyond models it is.

First a paper by the World Weather Attribution project (Nature July 2021) detailing a meta-analysis of existing modelled projections, which concluded that, on trend analysis alone, the spike in temperatures in the Pacific Northwest and British Columbia this Summer was virtually impossible without anthropogenic contributions. Second, an absolutely colossal wildfire, larger than all the other wildfires on the planet combined, raging in Siberia, where temperatures have been smashed, possibly somewhat exacerbated by a record-breaking summer in 2020, leading to drier conditions this year. It's worth remembering that Siberia is home to a massive amount of the world's permafrost, trapped in which is an abundance of methane, a gas whose absorption coefficient is 30 times that of CO2.

Then we have a report from the Potsdam Institute detailing the first objective measurement of the decline of AMOC - the Atlantic Meridional Overturning Circulation - coupled with the warning that it could be at a critical point. Also known colloquially as the 'North Atlantic Conveyor', this is responsible for the temperate climate in Northern Europe, among other climatic effects. As warm saltwater comes North and meets cold freshwater, the saltwater cools and dives down, continuing on around the cycle. For some considerable time, the amount of cold fresh water entering the North Atlantic has been increasing and accelerating, driving the interface between warm saltwater and cold freshwater further and further South. At some latitude, this section of the circulation system will simply shut off, potentially causing the advance of Arctic ice Southward.

And finally, a paper detailing an objective measurement of the Earth's insolation/radiation (energy input/output) budget and an analysis of contributing drivers showing unambiguously the effect of anthropogenic sources on global climate. This is, if one had seriously been needed by anybody, the absolute smoking gun of anthropogenic global warming.

It's here. It's now. We're in it.

That's the other shocking aspect of all this, to my mind. I've kept reasonably abreast of the current state of play for most of two decades, but I didn't see this coming this suddenly, this quickly. A perusal of recent literature - primary and grey - tells me I'm not alone in that. This is much earlier than we modelled for. Indeed, it's the sudden severity, coupled with how widespread the effects have been, that tells us unequivocally that we're in a new phase in the climate saga.

Predictably, there's much hand-wringing and pearl-clutching, but it isn't all bad news, and pragmatism is universally a better servant to science than hysteria. We all know what needs to be done. We have to cut carbon and hydrocarbon emissions. Radically.

There are some strategies we can bring to bear, of course. My first target would be to end fracking comprehensively by international treaty. Fracking is a significant source of atmospheric methane and other hydrocarbons, all highly absorbent greenhouse gases.

Switching to renewables is good, but the current state of play with (non-nuclear) renewables is such that it's unlikely to play anything like significant enough a role in addressing the current crisis. Bringing current renewables up to the necessary scale to meet our current needs if it had to replace fossil fuel is still some considerable way off.

Nuclear energy comes in two forms. The first, the one that people think of when you say 'nuclear' is fission - breaking apart. In a fission reaction, a quantity of fissile material - uranium, say - is bombarded with neutrons. A neutron smashes into the nucleus of a uranium atom, splitting it into an atom each of krypton and barium, with the release of a huge amount of energy and some free neutrons, which then go on to smash into other atoms, and so on. This is the famous nuclear chain reaction. That's if you want to build a bomb, of course. Uranium comes in more than one isotope, and that matters. U235 is highly unstable and prone to breaking apart if the nucleus is hit by a neutron. To build a bomb, you need a comparatively large amount of U325 than you do of U238, which is more stable. Highly refined or 'weapons-grade' uranium, then, is uranium with a high concentration of the more unstable U235, because the idea in a bomb is to get all the energy to release as quickly as possible (and in fact we have to use a bomb to increase the density even more to get the biggest yield). In a power station, you want all the energy, but at a more controlled rate, so uranium with an extremely low U235 ratio is the key. All the rest is basically boiling water to generate steam to drives turbines.

Fission has some drawbacks. First, the waste products of nuclear fission are not the sort of thing with which you'd want to be composting your prize petunias, although they'd definitely stand out from the competition, especially at night. Spent fuel rods are massively carcinogenic and difficult to keep isolated and incredibly problematic to store. Further, although highly safe under normal operating conditions, when things go wrong in a fission power station, they tend not to go wrong in any trivial sense. Nobody who's been around more than a few years won't have heard of Chernobyl, Windscale, Three Mile Island or Fukushima. It's worth noting that, despite popular contrivances and several documentaries and docudramas amplifying said contrivances, there was never any danger of a thermonuclear detonation in any of those instances. That's not to say that the release of radiation into the environment was anything but a bad thing, but the over-dramatisations do us no service.

Then there's the other form, nuclear fusion.

Fusion is really the holy grail of energy physics*.

Whereas fission requires smashing complicated radioactive atoms apart, fusion requires squashing simple atoms - the simplest, in fact; hydrogen - together. The result is an atom of helium and some energy. We can even see quite easily where the energy comes from.

Basically the mass of the helium atom is less than the two hydrogen atoms independently, even though they have exactly the same constituents. We can see this quite easily. We have 2 protons, at 1.673 x 10-27 kg each, 2 neutrons at 1.675 x 10-27 kg and 2 electrons at 9.109 x 10-31 kg. The helium atom has a mass of 6.646 x 10-27 kg. We don't even need to get the chalk out to see that just the four nucleons, at a total mass of 6.696 x 10-27 kg, add up to more than the entire helium atom, without even bringing the electrons into the mix. This extra mass is, via $E=mc^2$, where the energy comes from to drive our generators.

But there's a problem. On paper, this all looks really straightforward, but we've yet to make it work. And yet it also isn't theoretical, because this is the exact process that drives ALL our non-nuclear energy on Earth currently. The energy in radioactive materials is the exception, because those materials were formed in the deaths of earlier stars, but all other energy on Earth is derived from solar fusion. Stars have a slight advantage, though.

The big advantage they have is density (we can think of density and temperature as being approximately equivalent). In reality, it's extremely difficult to get nucleons to bond. Just getting them close enough to bond requires overcoming a repulsive force, the Coulomb barrier. Even at stellar energy densities, such interactions would statistically occur at a minuscule fraction of a percent required for stellar fusion to ignite were it not for a process known as quantum tunnelling, the same process that underpins the operation of the transistors and microchips in your internet device.

So how can we hope to achieve such densities on Earth? We can't make a star, surely?

No, but we have other means of containment at our disposal, as well as a battery of other tricks. Primarily, of course, containment is done by magnets. Tried and tested, this is our go-to for particle containment. It's how we keep lead ions going round in circles at the Large Hadron Collider, for example.

There are other ways we can nudge the process as well. In stars below about 1.4 times the mass of Sol, reaction is driven by a process known as the proton-proton reaction**, postulated by Arthur Eddington in 1920. It had actually been thought, prior to the discovery of quantum tunnelling, that the sun wasn't hot enough for fusion. The process is worth expending a little real estate on. Here's a nice diagram modified from Wikipedia.

It begins at the top, with two identical chains of reactions. On each chain, we start with two protons. Recall that an element is defined by the number of protons in the nucleus. An unbound proton, then, is a hydrogen ion, where an ion is an atom with an unbalanced number of electrons.

Two protons collide with a little help from quantum tunnelling. In the process of bonding, some energy is shed, converting one of the protons into a neutron and emitting a positron and a neutrino ($\nu$). We now have a new isotope containing one proton and one neutron, also a stable isotope of hydrogen. Unusually for an isotope, this one has its own name; deuterium.

Next, our deuterium ion collides with another proton. They bond, emitting a gamma ray ($\gamma$) and forming an isotope of helium composed of two protons and one neutron. Finally, the product collide, emitting two protons and forming a full helium nucleus (also known as an alpha particle ($\alpha$)).

This isn't an easy process to replicate, clearly, but we do have a neat little trick to aid us. specifically, we can press into a service another isotope of hydrogen that is incredibly rare in the natural world as it's quite unstable, but we can produce it pretty easily. It also has a name; tritium. This isotope has one proton and two neutrons in the nucleus, and can be produced by bombarding lithium 6 with neutrons, such as in a nuclear reactor, in a process known as neutron activation. As an aside, neutron activation is how all the carbon 14 (6 protons 8 neutrons) in our atmosphere is produced, as atoms of nitrogen 14 (7 protons 7 neutrons) get bombarded by neutron radiation from space, knocking out a proton and taking its place.

So the problems are known, and have been known for decades. As along as I've been eyeing this topic, it's been 'maybe a decade or two' away, but that's been quite a few decades already, and they've been saying that for a lot longer.

But now, something's changed.

Their experiment involves making a of pellet of fusion fuel, consisting of an amalgam of deuterium and tritium, and then firing a laser at it. The goal is to achieve 'ignition', which is pretty carefully defined as the output from fusion exceeding the energy expenditure in igniting it. Although this reaction technically exceeded the energy input, rendering a 1.3 megajoule (MJ) output from only 250 kilojoules (kJ) input, it hasn't quite met the requirements of ignition. Specifically, although the energy input into the pellet is an order of magnitude smaller than the output, the process requires conversion from UV to x-rays, which accounts for most of the energy. In order to get 250 kJ into the pellet, they had to output 1.9 MJ from the laser array.

Even so, this is a huge landmark, massively exceeding their previous record of 170 kJ output.

And this isn't the only recent landmark in fusion research, either. There have been major advances in magnetic containment, for example, but their explanation would take us too far afield for today's purposes.

As I mentioned, I've been watching fusion research for about as long as I've been watching physics. I know that, for all the time I've been watching, physicists have felt like fusion energy was just around the corner. A vague figure of something like 'the next ten or twenty years' has been the rolling chorus for the entire time. Back in 2008, popstar-cum-physicist Professor Brian Cox made a documentary for BBC's Horizon programme in which he spent an hour detailing fusion research, visiting K-Star and other fusion research facilities and, at the end, he said exactly what I'm saying here; that it's been a rolling ten or twenty years away.

He also said quite clearly that funding and appetite for fusion research is pitiful. A few simple comparisons put this into stark perspective, because they show what we can do when we pull out all the stops.

First, on 12th September 1962, at Rice Field in Houston Texas, John F. Kennedy stood in front of a crowd of mostly students and delivered a speech about the goals of a nation. It was a wonderful bit of rousing rhetoric penned by Ted Sorenson, one of the great speechwriters of the 20th century, and what it resulted in was spectacular beyond measure, and was the catalyst for much of the technological boom that followed it, but it all boiled down to two simple words.

In the last 20 months or so, the world has been faced with some incredible challenges and tough decisions. Not all of them have been met with the kind of resolve and dedication we deserve to expect but, due to strong motivation, a collaborative effort between science and industry and in getting bureaucracy out of the way, and the dedication and expertise of scientists and professionals from all spheres working together, we managed to get a range of effective vaccines out and distributed. We're not out of the woods yet, but we have reasons for some optimism (if we can rein our idiot politicians in a bit). Again, this can all be distilled to two simple words.

And now we need to find the fortitude to apply those two words again. When all is said and done, fusion is the only game in town when it comes to meeting all our energy challenges. Non-nuclear renewables are amazing, and will be especially of use in bringing energy to developing nations and remote areas, but in terms of scaling, as wonderful as they are, they're not even potentially in the same league.

In the final analysis, fusion energy is clean - the only by-products are, to a first approximation, hydrogen, helium and water. As an aside, it's well worth noting that we're also staring down the barrel of another crisis, a huge depletion in our resources of helium, not least because of its waste in balloons and silly voices. Helium is one of the few elements sufficiently light to escape into space, not incidentally, which is why it isn't abundant on Earth, despite being the second most abundant element in the universe. It's also an incredibly important resource for huge numbers of cooling and supercooling applications ranging from nuclear submarines to the superconductors for medical devices such as magnetic resonance imaging.

US astronauts got to the moon in eight years from almost a standing start. Effective vaccines were produced in a year from almost a standing start. In both cases all it took was two words. Fusion could have been achieved decades ago, I suspect, had those same two words been applied at the right time and with the right level of motivation and conviction.

We can have this, if we want it. We're not even going from a standing start. We're going from just before the finish line, because that really is how close these advances bring us. The problem is that the race has a time limit. If we don't reach this or a similar finish line before the race is ended, we're in real trouble. Current signs show that it could well be a photo finish.

OK, so my proclivities for stretching analogies way beyond utility aside, this is to my mind the best strategy for the longevity of our species, and to actually stand a chance of pulling back from the brink of our own disregard and stupidity.

Just two words, but can we say them? Can we mean them? What, exactly, did Kennedy say on that day in Texas? Did he say, 'Houston, we have a problem'? No, he did not. He said this:

We choose.